1. Field of Invention
The present invention relates to a sulfur vulcanizable novel butyl rubber and a rubber composition having an improved processability and vulcanized physical properties containing the same.
2. Description of the Related Art
Heretofore, butyl rubber is used as an inner liner, bladder of a tire, gasket, diagram, hose, belt, rubber vibration isolator, etc., utilizing the characteristics thereof (e.g., gas impermeability, vibration absorbance property). However, since butyl rubber accelerates the vulcanization, various attempts have been made to facilitate blending thereof with the other diene rubbers and various halogenated butyl rubbers having improved such properties. However, the butyl rubber has problem in that the weather resistance is not sufficient because the butyl rubber is of unsaturated type. Especially, the butyl rubber cannot be used as, for example, a sidewall of a tire, etc. Therefore, it has been proposed in U.S. patent application Ser. No. 88/199665 (or EP-A-344021) that butyl rubber is obtained by halogenating a copolymer containing p-alkyl styrene unit. This butyl rubber is surely excellent in the weather resistance etc., and therefore, the butyl rubber becomes usable as a tread, sidewall etc. of the tire. However, since the halogen group of the butyl rubber is highly reactive, the butyl rubber is reacted with other compounding agents such as silica and zinc oxide, and therefore, the new problem cause that, when silica is added, the viscosity is increased. Furthermore, when zinc oxide is initially compounded, there occurs a problem in that the zinc oxide is reacted with the butyl rubber. Thus, the timing at which zinc oxide is added should be limited. In addition, since this butyl rubber does not possess an unsaturated group, the vulcanization with sulfur is difficult and the covulcanization together with diene rubbers with sulfur are not possible in general, and therefore, the problems occur in the abrasion resistance, etc.